Process for the preparation of polyamides



Patented Nov. 26, 1940 UNITED STATES PROCESS FOR THE PREPARATION OF POLYAMIDES Wilb'ur A. Lazier, New Castle County, DeL, assignor to E. I. du Pont de Nemours 4i. Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 4, 1940, Serial No. 312,360

4 Claims. (Cl. 260 2) This invention relates to synthetic polymers and, more particularly, to the preparation of polymeric materials from dicarboxylic acid amides. I

i This application is a continuation-in-part of copending application= Serial No. 267,448, filed April 12, 19 39.

This'invention has as an object the preparation of polymeric amides. Another object is the 10 conversion to polyaniides of diamides derivable fromdicarboxylic acids in which the carboxyl groups are separated by at least four carbon atoms in contiguous relation. Other objects will be apparent from the reading of the following description of the invention.

These objects are accomplished by bringing a diamide derivable from a dicarboxylic acid in which the two carboxyl groups are separatedby at least four carbon atoms in contiguous relation and hydrogen into ontact with a hydrogenation catalyst at a. temperature between 200 and 450 C. and at a pressure in excess of 10 atmospheres.

The folowing examples set forth certain well defined instances of the application of this invention. They are, however, not to be considered as limitations thereof, since" many modifications may be made without departing from the spirit and scope of this invention.

' Example I Seventy-two parts by weight of adipamide,

10 parts of an active cobalt-on-alumina catalyst, and'35 parts of ammonia were charged into a steel shaker-tube and hydrogenation was allowed to proceedat 260 C. under a total pressure of 500 to 700 atmospheres. The pressure drop amounted to about 170 atmospheres in three hours. The tube was then cooled to room tem- 40 perature and its contents discharged. The catalyst was removed from the product by filtration. The latter was then distilled giving 3.6 parts of hexamethyleneimine, 7.6 parts of hexamethylenediamine, 7.5 parts of higher-boiling amines, and 27 parts of a clear non-volatile polymer which solidified ,when cooled. The heated polymer could be formed into any desired shape, which shape itretained on cooling. The warm polymer could also be spun, manually into fibers of very small diameter.

Example II A charge consisting of .72 parts by weight of sebacamide, 10 parts of an active nickel catalyst, 5 35 partsof liquid ammonia, and hydrogen was heated in an agitated steel tube at 260 C. under a total pressure of 600 to 650 atmospheres for three hours. The product was dissolved in methanol, the catalyst removed by filtration, and the filtrate distilled. After the removal of the meth- 6 anol at slightly reduced pressure, the pressure was reduced to 1 to 2 mm. and the temperature of the bath was increased to 275 C. After 20 to 30 minutes under these conditions only a small amount of material had collected on the walls 10 of the column, and no distillate was obtained. The polymeric residue, 56 parts, had a melting or softening point of 128 to 130 C. The product was manually spinnable, giving short fibers. An elementary analysis gave the values: %C, 69.8; '15 %H, 11.5; %N, 8.2. These values together with the fiber-forming prdperties of the polymeric product indicate that it is a polyamide, presumably a linear polyamide of the general type described in U. S. Patent 2,130,948. 20

The invention is applicable to any amide derivable from a dicarboxylic acid in which the two carboxyl groups are separated by at least four carbon atoms in contiguous relation. Thus, malonamide, succinamide, glutaramida phthal- 25 amide, and the like are not suitable for the preparation of polymeric products by the present process. Adipamide, however, is particularly suited for this purpose, as are also the amides derivable from mono-, di-, and poly-methyl so adipic acids, pimelic acid; suberic acid; azelaic acid; sebacic acid; hexadec ane-l, 16-dioic acid; 2-octyl sebacic acid; hydroaromatic dicarboxylic acids, e. g., hexahydroterephthalic and. decahydronaphthalene 1,5-dicarboxylic acids; cyclohex- 35 ane 1,2-diacetic acid; and the like.

The diamides may be prepared by any of the known methods; for example, by reacting the proper dicarboxylic acid or its ester, acid anhydride, or acid halide with ammonia at appro- 4o priate temperatures and pressures, or by treating the dicarboxylic acid with slightly more than nated as hydrogenation catalysts. These may consist of a hydrogenatlng component such ass.

2 v hydrogenating metal or metal oxide, together with a dehydration component such as a compound selected from the group known technically as dehydration catalysts. Examples of hydrogenation catalysts are reduced metals such as silver, copper, tin, cadmium, iron, cobalt, and nickel. These metallic catalysts may be promoted with oxide promoters such as aluminum oxide, manganese oxide, zinc oxide, magnesium oxide, or chromium oxide. The promoted catalysts may be physical mixtures or chemical compounds. The metallic catalysts may be used in the form of a powder. If a dehydration component is also used, it may be any of the well known dehydration catalysts; for example, alumina, chromium oxide, silica, thoria, kaolin, blue oxide of tungsten, etc. These may be in the form of supporting material for the catalyst. An illustration of such a catalyst is found in Example I, where cobalt is supported on alumina. Certain metallic oxides belong to the class of compounds known as diflicultly reducible oxides and have both hydrogenating and dehydrating properties. Such compounds come clearly within the class of catalysts that may be used in this invention. By the term diflicultly reducible is meant that the oxides are not substantially reduced to metal by prolonged exposure in a state of purity to the action of hydrogen at atmospheric pressure and at a temperature of 400 to 450 0. Such oxides suitable for the hydrogenation of amides are zinc oxide, manganese oxide, magnesium oxide, etc.

These oxides may be employed either alone or in combination with each other or with other oxides which have a promoting action. Preferably the oxide employed .as a promoter for the hydrogen ating metal or oxide has little activity of itself or is much less active than the hydrogenating oxide employed with it, yet it serves to further promote the activity of the more active oxide. I In the carrying out of this reaction temperatures within the range of from 200 to 450 C. have been found to be suitable. In general, however, it is preferred to operate within the temperature range of 225- to 300 C. The process is operable under pressures in excess of 10 atmospheres. Nevertheless, the reaction is not re-. stricted to any maximum pressure range and any pressure may be used which is within the meparting from the spirit and scope thereof, it is to chanical limits of the equipment employed. The hydrogenation reaction is faster at the higher pressures and for this reason a pressure range of from 100 to 1000 atmospheres is favored.

Since the product may contain volatile byc products in addition to the desired polymer it is necessary for most purposes to purify the polymer by heating in a vacuum to drive away volatile materials, by blowing with steam, nitrogen or other inert gas, by reprecipitation, or by other known methods of purification.

The process of this invention provides a. simple means for producing polymersfrom amides in one step.

A solvent is desirable in the carrying out-of the reaction, but is not necessary. Examples of suitable inert solvents are ammonia, cyclohexane, decalin, purified mineral oil, and the like. Of these ammonia is preferable.

The products of this invention may be used alone or in combination with other polymers, resins, plasticizers, pigments, dyes, etc.

As many apparently widely different embodiments of this invention may be made without debe understood that Ido not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process for the production of polymeric materials which comprises bringing a dicarboxylic acid diamide having at least four carbon atoms in contiguous relation between the car boxyl groups and hydrogen into contact with a hydrogenation catalyst at a temperature within the range of 200 to 450 C. and at a pressure in excess of 10 atmospheres.

2. The process in accordance with claim 1 characterized in that the reaction is carried out at a temperature within the range of 225 to 40 3. The process in accordance with claim 1 45 4. The process in accordance with claim 1 characterized in that the reaction is carried out in an inert solvent.

WlLBUR A. LAZIER. 

